Traditionally, usual yarns (yarns commonly used, such as a filament, false twist yarn or spun yarn) are often used as jointing yarns (binding yarns) for binding front and back faces together for three-dimensional structure knitted fabrics made using many types of weft knitting machines and warp knitting machines that have been proposed. These are mainly used for linings and the like of general materials and cloths, and have an effect of adding appropriate thermal insulation characteristics, but are poor in compressibility and compression recoverability.
Furthermore, a three-dimensional structure knitted fabric using a heat seal yarn as a binding yarn is known in the art, and examples of the three-dimensional structure knitted fabrics include a knitted fabric described in JP-A-4-240252. This knitted fabric is a mold product utilizing formability of the heat seal yarn, and is suitable for pressure forming such as heat press adequate for the formability, but has almost no compressibility and compression recoverability, and flattening resistance or the like under repeated loads is not considered.
Furthermore, for the example of a knitted fabric described in JP-A-7-316959, a circular corrugated knit using a connecting yarn in combination with a heat seal yarn and a highly crimped yarn is proposed. Use of polyurethane and the like in the connecting yarn is described in this publication. Furthermore, a three-dimensional knitted fabric using a binding yarn in combination with a heat seal yarn and a stretchable yarn (polyurethane based elastic fibers, etc.) is described in JP-A-2001-164444. They are to provide a cushioning property with the highly crimped yarn and the stretchable yarn and reduce flattening under repeated loads, but has a problem such that when the heat seal yarn is used in the connecting yarn, the low softening point of the heat seal yarn causes creases to occur in a substrate during dyeing processing and the like, the creases are not eliminated after finishing, and the heat seal yarn as a connecting yarn is heat-sealed to fix the front and back knitted fabrics, so that the knitted fabric as a whole has almost no stretchability, exhibits neither cushioning property nor flattening resistance by the effects of the highly crimped yarn and the stretchable yarn, is poor in compressibility and compression recoverability, and is flattened under repeated loads. Further, non-elastic fibers used in the connecting yarn and the ground knitted fabric are heat-sealed, so that the knitted fabric as a whole becomes rigid, and although finding some application for industrial materials, it is not suitable at all as a general material or sub-material worn by a person or used at a location close to a skin, and cannot be practically used in this field.
On the other hand, as a similar product, a three-layer structure knitted fabric manufactured by a double raschel machine, which is one type of warp knitted fabric, is commercially available. This knitted fabric uses a monofilament as a binding yarn. Use of the monofilament is intended for improving the cushioning property by means of its high degree of elasticity. However, this three-dimensional structure knitted fabric is rigid as a whole due to stiffness of the monofilament, and is therefore unsuitable as a fabric worn by a person as in the case described above.
JP-A-5-106146 describes a process of connecting one knitted fabric and the other knitted fabric with an elastic yarn, and using methods such as the increasing/decreasing of knitting courses achievable only by a flatbed knitting machine and partial knitting to knit a highly rugged and firm knitted fabric. However, the flatbed knitting machine has a rough gage, and therefore requires that several strings of yarn having a large size, for example bulky wool yarn or highly crimped thick synthetic fiber long finished yarn should be arranged for knitting, and the knitted fabric thus formed is a sweater or the like having rough stitches, and a dense and light knitted fabric desired in the present invention cannot be obtained. Furthermore, a stable shape cannot be retained even when the thickness of the binding yarn is increased because of the rough gage, and the warp and weft elongation balance of the knitted fabric is not satisfactory. Furthermore, the prior art has technological ideology of a method of three-dimensionally knitting a fabric along a silhouette of a human body, but has no concept of providing the knitted fabric itself with a three-dimensional structure having an air gap. Further, the flatbed knitting machine has a fatal problem such that a yarn feeding port travels to and fro along with a carriage, and a yarn is fed from the yarn feeding port and a knitting motion is repeated, but when an elastic yarn is knitted, the draw ratio varies along the width direction if using a bare string, thus making it impossible to obtain uniform stitches. Thus, it is common sense among those skilled in the art that no bare string is used, but so called a covering finished yarn with non-elastic fibers previously wound around a bare string of elastic yarn is used.
Furthermore, EP Patent Publication No. 431984 describes a knitted fabric for cloths allowing water in the body to be easily transpired to outside, having two knitted fabrics connected together with an elastic yarn, with the back face constituted by water repellent fibers alone and the front face constituted by water absorptive fibers and a platting-knitted elastic yarn. The purpose of using an elastic yarn for the front knitted fabric is to make stitches of the front knitted fabric denser to prevent the entrance of the outside air into the knitted fabric, and the technique is different from the present invention in both technological challenge and purpose. In the knitted fabric having this configuration, curling tends to occur because the front face and the back face have different degrees of stretchability, but use of an elastic yarn for the back face to add stretchability is not acceptable in view of its purpose. Specifically, if the elastic yarn is used for the back face to make the stitches denser in this knitted fabric, water in the body cannot be transferred through the knitted fabric, thus making it impossible to transpire water to the outside. Therefore, in the knitted fabric having this configuration, occurrence of curling cannot be inhibited, and a trouble arises in forming the knitted fabric into a cloth.
Furthermore, traditionally, when a bare string of polyurethane based elastic fibers is knitted by a circular knitting machine, all spandex based elastic fibers on the knitting machine can be fed to the knitting machine only at a same rate due to machine-related restriction, and if different weaves are to be knitted with polyurethane based elastic fibers, they can be knitted only at the, feed speeds relatively close to each other. As a result, polyurethane based elastic fibers suffer yarn breakage due to excessive drawing and fault drawing from a package of fibers due to insufficient drawing when the fibers are knitted. Consequently, weave-related restriction is significant, and knitting conditions are limited, so that the knitted fabric becomes too dense, and adequate stretchability cannot be obtained.